There isn't much You can do on the stock motors except the following;

COMPLETE COOL DOWN AFTER EACH FLIGHT !

That, and that alone is pretty much the ONLY thing and the BEST thing You can do to ensure longevity.

Some people oil, I don't; but if You do; not more than 1/100th of a drop.

They are cheap; replace them, or upgrade to the XTREME'S, they are serviceable in the way of brush replacement, but You will smoke them too if they get too hot.

Gary